1. Field of the Invention
The present invention relates to a printed-wiring-board holding apparatus and particularly to such an apparatus which applies suction or negative pressure to a printed wiring board (PWB) and thereby holds the PWB. A PWB on which electric components (e.g., electronic components) have been mounted should be called as a printed circuit board (PCB) but, in the present specification, a PCB is also referred to as a PWB, for avoiding complexity.
2. Discussion of Related Art
Generally, a PWB includes a thin substrate formed of an electrically insulating material such as a synthetic resin, and a circuit pattern formed of an electrically conductive material on the thin substrate. Thus, the PWB has flexibility. Therefore, when electric components (ECs) are mounted on the PWB, or when an adhesive or a creamed solder is applied to the PWB for mounting of ECs, the PWB cannot maintain an accurately flat posture, if a back surface of the PWB is not supported at a considerably large number of points.
To solve this problem, Japanese Patent Document No. 7-15189 teaches applying a negative pressure to a PWB and thereby holding the same. More specifically described, the document discloses a PWB holding apparatus including a base plate and a plurality of backup pins. The base plate has a plurality of negative-pressure supply holes each of which opens in an upper surface thereof and is connected via a passage formed therein to a negative-pressure supply source. Each of the backup pins includes an elongate pin portion and a container-like seat portion, and the pin portion has a passage which is formed therethrough in an axial direction thereof and is communicated with an inner space of the seat portion. Each backup pin is attached to the upper surface of the base plate, such that a lower-end surface of the seat portion thereof is held in close contact with a portion of the upper surface that surrounds the opening of a negative-pressure supply hole. In this state, the inner passage of the pin portion of the pin is communicated with the negative-pressure supply hole via the inner space of the seat portion, so that negative pressure is supplied to the inner passage to suck a PWB and thereby support the back or lower surface thereof.
The backup pins support the back surface of the PWB that is opposite to the front surface for which an operation, such as mounting of ECs, is performed. However, the backup pins must not engage uneven portions of the back surface of the PWB itself or the ECs mounted on the back surface. Therefore, the backup pins must be engaged with only limited portions of the back surface of the PWB and, depending upon those limited portions of the back surface, the backup pins must be attached to only limited portions of the upper surface of the base plate. Thus, the backup pins are attached to selected ones of the negative-pressure supply holes of the base plate, and the remaining supply holes to which the backup pins are not attached are covered with respective caps to avoid any leakage of the negative pressure.
However, it is cumbersome to attach the caps to the negative-pressure supply holes free of the backup pins, and accordingly it is time-consuming to attach the backup pins and the caps to the base plate and thereby set the PWB holding apparatus so that the apparatus can apply the negative pressure to a PWB and thereby hold the same.
The present invention provides a printed-wiring-board holding apparatus that has each feature described below. The following features are described, like claims, in respective paragraphs that are given respective sequential numbers. Any feature that includes another feature shall do so by referring to the number given to the latter feature. However, the following features and the appropriate combinations thereof are just examples to which the technical features, and the combinations thereof, described in the specification are by no means limited. In addition, in the case where one feature recites a plurality of items, it is not essentially required that all of those items be simultaneously employed in the one feature. That is, it is possible to select and employ only a portion (one, two, . . . , but not all) of those items.
(1) According to a first feature of the present invention, there is provided an apparatus for holding a printed wiring board, comprising a holding table which has a flat upper surface and a plurality of negative-pressure-supply holes each of which has an opening in the upper surface; at least one holding member which is attachable to the upper surface of the holding table such that a lower end surface of the holding member is held in close contact with a portion of the upper surface that surrounds the opening of at least one of the negative-pressure-supply holes, the holding member having a negative-pressure passage which is formed therethrough to connect between the lower end surface thereof and an upper end surface thereof, the holding member supporting, at the upper end surface thereof, the printed wiring board, and applying a negative pressure supplied from the at least one negative-pressure-supply hole via the negative-pressure passage thereof, to the board and thereby holding the board; and a plurality of opening and closing valves which are associated with the plurality of negative-pressure-supply holes, respectively, each of the opening and closing valves closing a corresponding one of the negative-pressure-supply holes in a state in which the holding member is not attached to the portion of the upper surface of the holding table that surrounds the opening of the corresponding one negative-pressure-supply hole, and opening the corresponding one hole, in a state in which the holding member is attached to the portion of the upper surface, so that the corresponding one hole is communicated with the negative-pressure passage of the holding member.
One holding member may be held in close contact with a portion of the upper surface of the holding table that surrounds the opening of one negative-pressure-supply hole, or the respective openings of two or more negative-pressure-supply holes. One or more holding members are attached to the holding table, at only one or more positions corresponding to one or more negative-pressure-supply holes selected from all the negative-pressure-supply holes of the holding table. The holding member or members attached to the holding table opens or open the opening and closing valve or valves, so that the selected negative-pressure-supply hole or holes is or are communicated with the negative-pressure passage or passages of the holding member or members and the negative pressure (i.e., vacuum or suction) is supplied from the negative-pressure-supply hole or holes to the negative-pressure passage or passages. Since the holding member supports, at its upper-end surface, the lower surface of the printed wiring board (PWB), the PWB does not sag; and since the holding member applies the negative pressure to the PWB and thereby holds the PWB, the PWB does not warp upward. That is, the holding member can hold a desired portion of the PWB such that the PWB does not warp in directions toward, and away from, the holding table. Regarding a negative-pressure-supply hole to which a holding member is not attached, the opening and closing valve associated with the hole remains closed to prevent leakage of the negative pressure. Thus, no plug or cap is needed to close the negative-pressure-supply hole to which no holding member is attached, unlike in a conventional PWB-holding device. That is, the present PWB holding apparatus can be easily set in a short time so that the holding apparatus can hold a desired portion of a PWB at a desired distance from the holding table.
(2) According to a second feature of the present invention that includes the first feature (1), the each opening and closing valve comprises a valve hole which is provided at an end portion of the corresponding one negative-pressure-supply hole on a side of the opening thereof in the upper surface of the holding table; a valve seat which is provided by a portion of the holding table and faces upward in the valve hole; a valve member which is provided in the valve hole and which closes the corresponding one hole in a state in which the valve member is seated on the valve seat; and a coming-off preventing portion which prevents the valve member from coming off the valve hole, at least the portion of the holding table being formed of a non-magnetic material, one of the valve member and a portion of the holding member in a vicinity of the lower end surface thereof being formed of a permanent magnet, and the other of the valve member and the portion of the holding member being formed of a ferromagnetic material.
At least a portion of the holding table that provides the valve seat is formed of a non-magnetic material. Therefore, irrespective of whether the valve member may be formed of a permanent magnet or a ferromagnetic material, the valve member is seated, because of its own weight, on the valve seat to close the opening and closing valve, in the state in which the holding member is not attached to the holding table. On the other hand, in the state in which the holding member is attached to the holding table, one of the valve member and the holding member that is formed of a ferromagnetic material is magnetized, and the valve member is attracted by the magnetic force to the holding member and is moved away from the valve seat, so that the opening and closing valve is opened. Since the valve hole is provided with the coming-off preventing portion, the valve member does not come off the valve hole, so that when the holding member is detached from the holding table, the valve member is seated, owing to its own weight, on the valve seat to close the valve. The valve member of an opening and closing valve which is associated with a negative-pressure-supply hole to which a holding member is not attached remains closed, so that when the hole is supplied with the negative pressure, the valve member is sucked owing to the negative pressure, and is seated on the valve seat, to prevent leakage of the negative pressure. The valve member may take any of known shapes such as sphere, hemisphere, cone, truncated cone, or cylinder having a hemispherical end portion or a truncated-conical end portion. In the case where the valve member has a hemispherical shape, a conical shape, a truncated-conical shape, or a cylindrical shape having a hemispherical end portion or a truncated-conical end portion, the valve member has, in one end portion thereof, a flat surface which is perpendicular to an axis line thereof and is to be attracted by a magnetic force, and is provided in the valve hole such that the flat surface is located on the side of the coming-off preventing portion. Since the flat surface of the valve member that is attracted by the portion of the holding member in the vicinity of its lower end surface has a large area, the valve member is attracted by a strong magnetic force. In the case where the valve member has a shape having an orientation, such as a semispherical shape, that is, the valve member includes a first portion designed to seat on the valve seat and a second portion designed to engage the coming-off preventing portion, it is desirable that the first and second portions of the valve member be not inclined relative to the valve seat, that is, the orientation of the valve member relative to the valve seat be maintained, notwithstanding the valve member is iteratively seated on and off the valve seat. That is, it is desirable to employ an inclination preventing device which prevents the valve member from being inclined relative to the valve seat. For example, if a distance between the flat surface of the valve member and the coming-off preventing portion is short, the engagement of those two elements prevents the valve member from being inclined, so that the valve member may be seated, without being inclined, on the valve seat to close assuredly the opening and closing valve. In this case, the flat surface of the valve member cooperates with a surface of the coming-off preventing portion that engages the flat surface to provide the inclination preventing device. Alternatively, it is possible to provide a small space between an outer surface of the valve member and an inner surface defining the valve hole, so that those two surfaces engage each other and thereby prevent the valve member from being inclined. In the latter case, those two surfaces cooperate with each other to provide the inclination preventing device. In the case where the valve member has a conical shape, a truncated-conical shape, or a shape including a truncated-conical end portion and a cylindrical end portion, it is desirable that a distance between a seat portion of the valve member that is seated on the valve seat and one end portion of the valve member that is opposite to the other end portion thereof located on the side of the coming-off preventing portion, as measured in a direction parallel to the axis line of the valve member, be longer than a distance between the seat portion and the other end portion. In the last case, the valve member hangs, at the seat portion thereof, on the valve seat, owing to its own weight, such that the axis line of the valve member is not inclined relative to the valve seat. The seat portion of the valve member cooperates with a portion thereof between the seat portion and the one end portion thereof to provide the inclination preventing device.
(3) According to a third feature of the present invention that includes the second feature (2), the portion of the holding member is formed of the permanent magnet, and the valve member is formed of the ferromagnetic material.
In many cases, the portion of the holding member in the vicinity of its lower end surface is larger than the valve member. Therefore, according to the present feature, the larger magnet produces a larger magnetic force, so that the valve member can be reliably moved away from the valve seat.
In addition, since the valve member is formed of a ferromagnetic material, the coming-off preventing portion may be also formed of a ferromagnetic material. When the coming-off preventing portion is magnetized by the permanent magnet of the holding member, the valve member formed of ferromagnetic material is attracted to the preventing portion, so that the valve member is reliably moved away from the valve seat. In particular, in a case, described later, where a coming-off preventing plate formed of ferromagnetic material is fixed to a main member of the holding table that is formed of non-magnetic material, and a portion of the preventing plate that corresponds to the valve hole functions as the coming-off preventing portion, the coming-off preventing plate is magnetized by the permanent magnet that provides the portion of the holding member in the vicinity of its lower end surface, so that the holding member is fixed with a sufficiently great magnetic force to the preventing plate, and the valve member is attracted to the magnetized preventing plate to open the opening and closing valve.
Moreover, the valve member enjoys a high degree of freedom with respect to its shape. In the case where the valve member is formed of a permanent magnet, it is essentially required that the orientation of magnetic poles of the permanent magnet be not changed even if the valve member is iteratively seated on and off the valve seat. On the other hand, in the case where the valve member is formed of a ferromagnetic material, it does not matter with the orientation of the valve member, that is, the phase of the valve member may change each time the valve member is seated on or off the valve seat. Thus, the shape of the valve member can be freely designed. In the case where the valve member is formed of permanent magnet, it is desirable to employ an orientation maintaining device which maintains an orientation of the valve member and thereby prevents an orientation of the magnetic poles of the permanent magnet from being changed. For example, in the case where the valve member has a shape having an orientation, such as a cylindrical shape having a hemispherical end portion, it is possible to employ the inclination preventing device as explained in connection with the second feature (2), so that the inclination preventing device prevents the valve member from being inclined and accordingly being rotated, and thereby prevents the orientation of the magnetic poles of the permanent magnet. The orientation maintaining device may be provided separately from the inclination preventing device, in addition to, or in place of, the same.
(4) According to a fourth feature of the present invention that includes the second or third features (2) or (3), the valve member comprises a spherical member.
If the valve member is provided by a spherical member, the spherical member is easily seated on the valve seat to close reliably the opening and closing valve. In addition, since the valve member may be provided by a commercially available steel ball, the valve can be produced at low cost.
(5) According to a fifth feature of the present invention that includes any one of the second to fourth features (2) to (4), the coming-off preventing portion comprises a coming-off preventing member which covers the opening of the corresponding one negative-pressure-supply hole, which is engageable with the valve member to prevent the valve member from coming off the valve hole, and which has at least one communication hole which is not closed by the valve member engaged with the coming-off preventing member, and keeps the communication between the corresponding one hole and the negative-pressure passage of the holding member.
The coming-off preventing member may have either one communication hole, or a plurality of communication holes. The shape of the communication hole or holes may be one of various known shapes, such as a circular or sectorial shape.
The negative pressure is supplied from the negative-pressure-supply hole to the negative-pressure passage via the communication hole or holes.
(6) According to a sixth feature of the present invention that includes the fifth feature (5), the portion of the holding member is formed of the permanent magnet, and the coming-off preventing member is formed of a ferromagnetic material.
If the holding member is placed on the holding table, the valve member and the coming-off preventing member are magnetized, so that the valve member is attracted to the preventing member, and the holding member is also attracted to the valve member and the preventing member and is fixed to the holding table. The coming-off preventing member and the valve member, both formed of ferromagnetic material, cooperate with a portion of the holding member that is formed of permanent magnet, to provide a fixing device. Otherwise, the holding member may be fixed to the holding table, with a different fixing device such as a bolt. However, it is cumbersome to use the latter fixing device to fix the holding member to the holding table. In contrast, since the magnetic force is used to fix the holding member to the holding table, it is just needed to place the holding member on the holding table, which assures that the holding member is easily attached to the holding table in a short time.
In the state in which the holding member holds the PWB, the holding member is strongly fixed, owing to the negative pressure, to the holding table. The lower end of the holding member is held in close contact with a portion of the upper surface of the holding table that surrounds the opening of a negative-pressure-supply hole. When the negative pressure supplied to the negative-pressure passage is applied to the PWB, the negative pressure is also applied to the holding member, so that the holding table holds the holding member. This holding function may be positively utilized in a state in which the holding member is not holding a PWB. To this end, for example, a flow restrictor is provided in the negative-pressure passage formed through the holding member. In the state in which the holding member is not holding a PWB, air flows into the negative-pressure passage via the upper open end of the holding member, while the flow restrictor restricts the amount of incoming flow of the air. Thus, a sufficiently great negative pressure is produced in an inner space of the lower end portion of the holding member that is adapted to contact closely the hole-opening surrounding portion of the upper surface of the holding table.
(7) According to a seventh feature of the present invention that includes the fifth or sixth feature (5) (6), wherein the coming-off preventing member has, in a lower surface thereof, a positioning recess which accommodates at least a portion of the valve member and thereby positions the valve member relative to the valve hole.
According to this feature, in a state in which the coming-off preventing member prevents the valve member from coming off the valve hole, the valve member may be positioned relative to the communication hole in a radial direction of the valve hole. Thus, the communication hole is not closed by the valve member, and the communication between the negative-pressure-supply hole and the negative-pressure passage is reliably maintained.
(8) According to an eighth feature of the present invention that includes any one of the fifth to seventh features (5) to (7), the coming-off preventing member comprises a coming-off preventing plate which is fixed to the upper surface of the holding table and covers the respective valve holes of at least two opening and closing valves associated with at least a portion of the plurality of negative-pressure-supply holes.
The coming-off preventing plate may have a size which can cover a plurality of valve holes corresponding to all the negative-pressure-supply holes, or a size which can cover a plurality of valve holes corresponding to a portion of the negative-pressure-supply holes.
According to this feature, a portion of the coming-off preventing plate that corresponds to a valve hole functions as a coming-off preventing portion. If a portion of the holding member in the vicinity of its lower end surface is formed of permanent magnet, the valve member is formed of ferromagnetic material, and the coming-off preventing plate is also formed of ferromagnetic material, the holding member is fixed to the holding table with a sufficiently great magnetic force produced by the preventing plate formed of ferromagnetic material.
Since the single coming-off preventing plate can cover a plurality of valve holes, the preventing plate can be easily attached to the holding table.
(9) According to a ninth feature of the present invention that includes the first feature (1), the each opening and closing valve comprises a valve hole which is provided at an end portion of the corresponding one negative-pressure-supply hole on a side of the opening thereof and which has a diameter greater than a diameter of the one negative-pressure-supply hole; a valve-seat member which is fixedly provided on the holding table such that the valve-seat member covers an opening of the valve hole and which has a through-hole formed therethrough and a valve seat formed around the through-hole; a valve member which is provided in the valve hole such that the valve member is movable to a closing position where the valve member is seated on the valve seat and to an opening position where the valve member is away from the valve seat; a spring member which applies a biasing force to the valve member in a direction toward the valve seat; and a valve-opening projection which projects from one of the holding member and the valve member, and which engages, in a state in which the holding member is held in close contact with the portion of the upper surface of the holding table that surrounds the opening of the corresponding one hole, the other of the holding member and the valve member to position the valve member at the opening position against the biasing force of the spring member, and allows the valve member to be positioned at the closing position by the biasing force of the spring member in a state in which the holding member is not held in close contact with the portion of the upper surface of the holding table.
The PWB holding apparatus according to this feature is operated such that in the state in which the holding member is attached to the holding table, the valve-opening projection engages the other of the holding member and the valve member, so that the valve member is moved away from the valve seat and the negative-pressure passage is communicated with the negative-pressure-supply hole. In the state in which the holding member is not attached to the holding table, the valve member is seated on the valve seat to close the opening and closing valve. Thus, it is not needed to close, with one or more closure members, one or more negative-pressure-supply holes to which no holding members are attached. Thus, the PWB holding apparatus can be easily set in a short time such that the holding apparatus can hold one or more desired portions of the PWB at a a desired distance from the holding table.
(10) According to a tenth feature of the present invention that includes the ninth feature (9), the valve-opening projection projects from the valve member such that in a state in which the valve member is seated on the valve seat, the projection extends through the through-hole of the valve-seat member and a free end portion of the projection is located outside the through-hole.
(11) According to an eleventh feature of the present invention that includes the ninth feature (9), the valve-opening projection projects downward from the holding member such that a free end portion of the projection is located below the lower end surface of the holding member, and such that in the state in which the holding member is attached to the holding table, the projection extends through the through-hole of the valve-seat member, projects into the valve hole, and pushes the valve member away from the valve seat against the biasing force of the spring member.
So long as the valve-opening projection fits in the through-hole, the communication between the negative-pressure-supply hole of the holding table and the negative-pressure passage of the holding member is maintained. Thus, the valve-opening projection also functions as a communication-maintaining projection.
(12) According to a twelfth feature of the present invention that includes any one of the second to eleventh features (2) to (11), the each opening and closing valve further comprises a sealing member which prevents, in a state in which the valve member is seated on the valve seat, the negative pressure from leaking from between the valve member and the valve seat.
(13) According to a thirteenth feature of the present invention that includes the twelfth feature (12), the sealing member comprises a pad which is formed of a material softer than a material used to form the valve seat and which covers the valve seat.
The pad may be formed of a synthetic resin or a rubber.
When the holding member is detached from the holding table, the valve member is seated on the valve seat via the pad. Therefore, the opening and closing valve recited in any one of the second to eighth features (2) to (8) is operated such that in the state in which the negative pressure is supplied to the negative-pressure-supply hole, the valve member is sucked owing to the negative pressure, and pressed on the pad, so that the pad is deformed and accordingly is closely contacted with the valve member. Thus, the leakage of the negative pressure is more reliably prevented. In addition, the opening and closing valve recited in any one of the ninth to eleventh features (9) to (11) is operated such that the valve member is pressed, owing to the biasing action of the spring member, on the pad to prevent more reliably the leakage of the negative pressure. The valve member may be covered by a pad, in addition to, or in place of the valve seat being covered by a pad.
(14) According to a thirteenth feature of the present invention that includes the twelfth feature (12), the sealing member comprises an O-ring.
The O-ring may be one which is independent of the valve seat, or one which also functions as the valve seat. In addition, the O-ring may be one which is provided on the valve member, or one which is provided in the valve hole.
In the case where the O-ring is independent of the valve seat, the valve member contacts the O-ring when the valve member is seated on the valve seat provided in the valve hole to close the opening and closing valve. The valve member is pressed against the O-ring by the attraction applied to the valve member owing to the negative pressure or the biasing action of the spring member. The O-ring is elastically deformed and held in close contact with the valve member, so that the leakage of the negative pressure is assuredly prevented. The seating of the valve member on the valve seat defines the limit of elastic deformation of the O-ring, so that the O-ring is prevented from being excessively elastically deformed and the sealing function of the same is prevented from being lowered.
In the case where the O-ring functions as the valve seat, the O-ring is contacted with the valve member and the inner wall surface defining the valve hole. The valve member is seated, by the attraction applied thereto owing to the negative pressure or the biasing action of the spring member, on the O-ring while elastically deforming the same. Thus, the opening and closing valve is closed, and the leakage of the negative pressure is prevented by the O-ring.
(15) According to a fifteenth feature of the present invention that includes any one of the twelfth to fourteenth features (12) to (14), at least a surface of at least one of the valve member and the sealing member is formed of a sticking-preventing material.
Since at least a surface of at least one of the valve member and the sealing member is formed of a sticking-preventing material, the sticking-preventing material prevents a problem that the valve member is stuck to the sealing member, the opening and closing cannot be opened, and the PWB cannot be held. The sticking-preventing material may be a first material which is more chemically stable than a material used to form the sealing member, such as rubber or its analogous material; or a second material which has a lower friction coefficient than that of a material used to form the sealing member. The above first material is effective in preventing the valve member from being stuck to the sealing member in the case where the valve member is kept in contact with the sealing member for a long time. The above second material is effective in preventing the valve member from being stuck to the sealing member in the case where the valve member is contacted with, and separated from, the sealing member so frequently. In the case where only a surface of the valve member or the sealing member is formed of the sticking-preventing material, a layer of the sticking-preventing material is formed on a surface of a base material, and the sticking-preventing layer is formed of a material which is more chemically stable, or has a lower friction coefficient, than the base material. The sticking-preventing material may be polytetrafluoroethylene (PTFE), which is chemically stable and has a low friction coefficient.
(16) According to a sixteenth feature of the present invention that includes any one of the first to fifteenth features (1) to (15), the plurality of negative-pressure-supply holes open in the upper surface of the holding table, such that the respective openings of the negative-pressure-supply holes are substantially uniformly distributed and substantially regularly arranged.
Even though the distribution of a plurality of portions of a PWB that are to be held by a plurality of holding members may be irregular, those holding members can be attached to respective positions corresponding to appropriate ones of the negative-pressure-supply holes substantially uniformly and substantially regularly arranged, and can cooperate with each other to hold the PWB.
(17) According to a seventeenth feature of the present invention that includes any one of the first to sixteenth features (1) to (16), the holding member includes a shank portion which supports, at an upper end surface thereof, the printed wiring board; and a suction cup which is formed of a flexible material such as rubber and is attached to an upper end portion of the shank portion such that the suction cup surrounds the upper end surface of the shank portion and closely contacts the printed wiring board.
The suction cup prevents the leakage of the negative pressure through the interface between the holding member and the PWB, so that the holding member can more reliably hold the PWB.
(18) According to an eighteenth feature of the present invention that includes any one of the first to seventeenth features (1) to (17), a lower end portion of the holding member provides a seat portion which has a connection recess opening in a lower surface thereof such that an area of an opening of the connection recess in the lower surface is not less than two times larger than an area of the opening of the corresponding one negative-pressure-supply hole in the upper surface of the holding table.
A portion of the holding member that holds the PWB may be connected to a middle portion of the seat portion or a different portion of the seat portion than the middle portion.
The holding member can be attached to an arbitrary position on the holding table, within a range in which the connection recess of the holding member can be aligned with the opening of one negative-pressure-supply hole. Thus, the position where the holding member attached to the one negative-pressure-supply hole holds the PWB can be changed. That is, even if the holding table may not have a negative-pressure-supply hole at a position just corresponding to a portion of the PWB that is to be held by a holding member, that portion of the PWB can be held by a holding member which is attached to an appropriate one of the negative-pressure-supply holes. Thus, the total number of the negative-pressure-supply holes can be decreased.